Abstract

In this study, the surfaces of membranes are modified with custom-designed polymers for separation of water-oil mixture. By tuning the chemical structure of the polymers, the water and oil repellencies of the membrane can be tailored. In particular, two types of membranes have been made and used to construct a continuous water-oil separator: one allows oil to pass but stops water, and the other allows water to pass but stops oil. The continuous water-oil separator splits one stream of water-oil mixture into two streams: a water stream that has less than 0.075 wt% of oil, and an oil stream that has less than 0.01 wt% of water.Because of the surface texture of the membranes, the modified membranes possess extreme repellencies to either water or oil while can be completely wetted by the other liquid. The two types of membranes used in the water-oil separator are (i) superhydrophilic but superoleophobic (denote as HBO) and (ii) superoleophilic but superhydrphobic (denote as OBH). The super hydro/oleo-philicity and hydro/oleo-phobicity are characterized and explained by Wenzel and Cassie-Baxter models. In addition, the robustness of the hydro/oleo-philic and hydro/oleo-phobic states is analyzed, and critical parameters that affect the robustness of these states are determined.The performance of the membranes during the separation of water-oil mixture is characterized by measuring (i) the relationship between pressure and volume flux, (ii) break-down pressure, (iii) break-down time, and (iv) the oil (water) percentage in the water (oil) stream after separation. These parameters provide guidance to the design and operation of the continuous water-oil separator.